Sputtering material from a target to cover a substrate has become common practice in a wide range of technical fields such as integrated circuit manufacture, large area glass coating and nowadays more and more for the coating of flat panel displays. Such sputtering takes place under a reduced pressure atmosphere wherein sputtering or reactive gases or mixtures of both are admitted in a controlled way. Free electrons hopping in a magnetically confined racetrack ionise the gas atoms or molecules in the vicinity of the target surface. These ions are subsequently accelerated towards the target that is negatively biased, thereby dislodging the target atoms and giving them enough kinetic energy to reach the substrate and coat it. The shape of the racetrack is defined by a static magnetic array, close to that target surface that is opposite to the surface that is being sputtered. Such a deposition process is commonly called “magnetron sputtering” due to the presence of the magnetic array.
A plethora of apparatus has been developed, designed and built with a specific application in mind. The first, smaller magnetron sputtering apparatus used stationary planar targets initially prevalently circular in form (i.e. like the silicon wafer that was sputtered upon). Later also elongated, rectangular shapes for coating of larger substrates that pass under the target became available (e.g. as described in U.S. Pat. No. 3,878,085). Such elongated planar targets are now commonly used in dedicated ‘display coaters’ for the manufacturing of flat panel displays like liquid crystal displays (LCD) and plasma screens. These planar targets are usually mounted in the access doors of the apparatus; the target surface being easily accessible (with doors open) and spanning the length of and even extending over the substrate width. In a display coater the substrate to be coated is held under a slant angle (7° to 15°) out of the vertical and leans on a conveying system. As the target must be parallel to the substrate in order to obtain a uniform coating, the target must be mounted under substantially the same angle.
Stationary targets are easy to cool and energise (as they are static with respect to the apparatus), but they have the disadvantage that the target material is only eroded away beneath the racetrack. The useable lifetime of the target thus being limited to that point in time just before the target is first punctured. The problem of non-uniform erosion can be dealt with by introducing a magnet array that rotates relative to the target surface (such as e.g. introduced in U.S. Pat. No. 4,995,958 for circular planar magnetrons) or that translates relative to the target surface (such as e.g. described in U.S. Pat. No. 6,322,679 for elongated planar magnetrons). Such constructions—although alleviating the uneven erosion problem to a great extent—make the system more complex.
Large area coaters to coat e.g. window glass with all kinds of stacks of functional coatings are usually equipped with a rotating, tubular sputtering target. In this application the economic driver is throughput at a low material cost and a good quality. Rotating tubular targets are the ideal choice for that, as they can span large widths and can be used for a long period of time. The trade-off is that the target itself is rotating relative to the apparatus and hence a complex and space occupying ‘end-block’ is needed to bear, rotate, energise, cool and isolate (coolant, air and electricity) the rotating target while holding the magnet array fixed inside. Two types of arrangement exist:                Double, right-angled end-blocks such as disclosed in U.S. Pat. No. 5,096,562 (FIG. 2, FIG. 6) and US 2003/0136672 A1 wherein the means for bearing, rotating, energising, cooling and isolation (air, coolant and electrical) are divided between two blocks, situated at either end of the target. With right-angled is meant that the end-blocks are mounted to the wall that is parallel to the rotation axis of the target. These end-blocks are usually mounted at the bottom of a top-box containing ancillary equipment. The top-box with end-blocks and mounted target can be lifted in its entirety out of the large area coater for easy target replacement and servicing.        Single, straight-through end-blocks such as disclosed in U.S. Pat. No. 5,200,049 (FIG. 1) wherein the means for bearing, rotating, energising, cooling and isolation are all incorporated in one end-block and the target is held cantilevered inside the large area coater. With ‘straight-through’ is meant that the rotation axis of the target is perpendicular to the wall on which the end-block is mounted. ‘Semi-cantilevered’ arrangements are also described (U.S. Pat. No. 5,620,577) in that the end of the target farthest from the end-block is held by a mechanical support (without any other functionalities incorporated in that support).Although rotatable targets could have many advantages when used for display coaters (increased uptime, nearly 100% target usage) the mounting of these targets poses problems:        Either one opts for a single or double right-angle end-block that is mounted to the door. But in that case a substantial part of the door length is occupied by the end-blocks, so that the usable target length does not span the width of the substrate.        Or one opts for a single straight-trough end-block, but in that case, radical modification of the display coater is needed inhibiting the introduction of such an end-block.One is thus faced with a dimensional constraint problem. A first possible solution—described in WO 2005/005682 A1—reduces the width of the end-blocks by incorporating their functionalities inside the target tube. Although this solution is perfectly well possible the inventors sought for further possibilities in size reduction and came up with the invention, described in what follows, that solves the dimensional constraint problem.        